The present invention relates to extrema coding, and in particular, to the use of a noisy limiting-amplifier in an extrema coding application. Even more particulary, the present invention relates to the use of commonly available limiting-amplifier integrated circuits or other integrated circuits having limiter circuits as one of their subcircuits. The basic extrema coding principle can be found in U.S. Pat. No. 4,545,065.
In extrema coding, an analog signal having broadband noise superimposed thereof or into which broadband noise is added, is first subjected to a preemphasis operation, generally differentiation, to encode the extrema points of the original analog waveform and the noise (i.e., the maximum and minimum points) as zero crossings. The zero crossings, which represent the extrema, are then encoded by an infinite clipping circuit having a high bandwidth relative to the original analog signal so as to create a binary or two-level signal. This binary or two-level signal contains substantially all of the information necessary to reproduce the original analog signal. In order to reproduce the original analog signal from the encoded signal, a filter, typically an integration stage, may be used. It has been theorized that the human ear performs this integration function naturally, so that an extrema coded signal supplied to the human ear will sound substantially the same as the original unencoded analog signal. It has also been theorized that the extrema coding principle also applies to the remainder of the human perception system, for example, the human visual system, so that an extrema encoded signal representing video information supplied to the human eye by a display device will also appear substantially the same as the original analog signal when supplied to the display device.
Various applications of extrema coding are possible, including bandwidth compression, coder-decoders (CODEC's), signal transmission across noisy channels, low bit rate data transmission and hearing aids and hearing protectors.